In most cases you should be using M4 zinc plated or stainless steel machine screws for your home hardware. Any type of head is suitable, but it is most common to use machine screws with a pan head, truss head, or round head design. Our hardware comes with pan head or truss head M4 machine screws by default.
If you are in an area of high humidity/salt content (on the coast for example) then you should consider stainless steel over zinc plated.
What are Machine Screws?
Machine screws are primarily intended for fixing two or more parts together. This can be done by screwing directly from one part into another (for instance, to secure a metal drawer handle to a wooden drawer). Or, through the use of a nut to hold the pieces together (for example, two thin pieces of metal could be held together with a machine screw and nut).
Note that machine screws can only be used in tapped holes or with a suitable nut.
Machine screws appear similar to regular screws - they both feature a threaded shank, and both often use the same type of head. However, whilst a regular screw has a pointed end to allow it to be driven into timber etc, a machine screw is cut at 90 degrees so as to allow it to easily thread into other parts.
Machine screws can have both a traditional and recessed design. The former of which results in the head sticking out when fastened in place. The latter results in the screw sitting flush when fastened in place.
Machine Screw Sizing
Machine screw sizing is quite simple - the letter M followed by a number. The M stands for machine screw, and the following number stands for the nominal diameter of the screw.
For instance, M4 states that the screw is a machine screw with a nominal diameter of 4mm.
Machine screws are commonly found in sizes from M1 to M12. However, other sizes are also available and screws as small as M0.5 (a nominal diameter of 0.5mm) are manufactured.
For your home hardware (knobs, handles etc) you will most likely be using M4 machine screws. This is also the size of machine screw that we use with all of our hardware products (except for a few products that use self-tapping screws).
Machine Screw Materials, Platings & Finishes
Machine screws can be made out of a number of different materials such as steel, stainless steel, titanium, nylon and others. This base material may then be plated or otherwise coated (often to increase corrosion resistance). Each material offers different features, and the cost is different. However, for home hardware indoor use it's really only required to go with steel or possibly stainless steel.
Steel Machine Screws: These are the most affordable screws and are made from freely available elements such as iron and carbon. Steel screws will rust easily, and must therefore be plated or coated to prevent this. The most common plating for steel screws is Zinc as it's a budget friendly option whilst also providing decent protection indoors. You can also use galvanized machine screws (these tend to offer greater protection) but ensure they are hot dipped and not cold dipped galvanized.
Stainless Steel Machine Screws: As the name implies, these are made from stainless steel. Most likely from 304 stainless steel (304SS) but they could also be made from a lower grade such as 201SS, or a higher grade such as 316SS. For general indoor use it doesn't really matter which grade you go for. However, if you're using them somewhere humid (perhaps a bathroom) or if you intend on using the screws outside, then you should ensure you're at least using 304SS.
Note that the cost from the factory of zinc plated machine screws is about half that of 304 stainless steel screws. We don't have information on the difference in retail pricing though.
Points of Interest
What is a Tapped Hole?
A tapped hole is simply a hole that has been internally threaded. This threading allows for a threaded fastener to be inserted and held in place.
What are the Three Parts of A Screw?
A screw has three parts - the head (top of the screw), shank (middle part) and point (the end of the screw). All three parts can be designed differently.
For example, the head can be a pan head, truss head or other type. It can be a traditional design and sit with the head showing, or a recessed design in which the head sits flush. Furthermore, the head can feature a number of different screw drives, such as Phillips (often referred to as cross head), slotted, square and so on.
The shank can can vary in length and diameter. It can be threaded in various ways, such as course threaded, fine threaded, or perhaps threaded for machine use.
The point of the screw is the first part that makes contact with what you are fastening into. It can have a sharp tip (to help drive into timber for example), or be cut at 90 degrees as is the case for machine screws.
There are literally hundreds of different screw designs, so we won't go into every possibly type of head, shank and point design here.
The Nominal Diameter of a Machine Screw. What Does This Mean?
The nominal diameter of a screw is more of a label rather than an exact measurement. Realistically, the actual diameter of a machine screw will be slightly less than the nominal measurement so as to allow it to screw in without becoming stuck.
For example, an M4 screw has a nominal diameter of 4mm. However, the actual diameter may be between 3.85 and 3.95mm.
Why Are My Zinc Plated Screws a Different Colour?
The colour of your zinc plated screws might be yellow/gold, clear (often appears silver), blue, or possibly even black/green in colour.
The difference in colour is due to a difference in makeup of the zinc plating. Yellow/gold plating tends to offer better protection when compared to clear or blue. Black zinc plating is somewhere in the middle.
For indoor use it doesn't really matter which colour you go for as the protection offered by all types should be suitable. Perhaps, if you are in a humid environment or living on the coast you may consider going with yellow or moving up to stainless steel.
